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slydog

Exhaust design thread...

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OK so I need a new exhaust for the ute and have got some help and a couple of solid offers from to very good repped shops Stuart Vale @ Racers Choice and Tony @ Tuff Pipes.

 

Stu wanted to see a twin 2.5"system based on the Pacemaker extractors with a merged tapered 2 into 1 collector out to 3.5"and back down into a another merge tapper collector to split it out into the twin 2.5.

 

Tony was after a more traditional approach and reckons a well designed 3" will do up to 500hp with good collectors and pipe work.He did the pipes for ONBOC and many others in his time.

 

Fair enough both have there beliefs...Stu explained that modern V6 Commonwhores have twin 2.5's standard which sort of sold me after seeing all the new cars with twin systems.But I do know Mossy runs a single 3.5" and he loves it.Made the car quieter and a smoother sound at low RPM but at full noise is a different story of course.

 

Which then leaves me with a 2x2.5" Aero Chamber mufflers and a complete 3" that doesn't fit my ute any more thanks to the 2 tailshaft loops and the 4 link.So with Stuey OK to supply the collectors and pipeing If needed I guess I'll go ahead down that route and make it @ home with his or home made or other collectors but based on his design plans.Yes $2000 worth of carbies and stuff hits the bank VERY hard so $$$ saving on this part is OK as I can fab it @ home...but it has to be right.

 

Basic 2 into 1 collector...

 

Ebaycollectors_zpsebed4566.jpg

 

Weld tech's...

PerformanceHeaders1_zps8e8b6e2f.jpg

Performanceheaders_zpsb3b05edd.jpg

 

And the best been Burns...so they say

 

Burnscollector_zpsd0cd33a6.jpg

 

Sure look the goods ^^^ the Burns units do but I reckon it's stuff I/we can do @ home with the right tooling/knowledge/components and research.

 

So do anyone here run a merge tapered exhaust? Do you like it,who did it? and what was the formula used to sort it out? I know the longer the taper the better it should perform and TBH it has been done on motorbikes for years and years but hasn't made a huge impact in cars till the last 5 or so years I'd suggest.  

 

Any ideas or thoughts...put em in here,6cyl,V8 lawnmower whatever.

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For a high rpm engine like yours I reckon 2 1/4" secondaries, long enough to give you the cubic inch volume of your engine (250 = 2 pipes with 125cu in in each pipe) then merged into a 4" expansion chamber (3.5 if space is tight)  down to the original muffler position where you taper it back to 3" and into a straight through maximum flow hookers or if you have the coin a Borla straight through circle track muffler - dumped at the diff.  It may sound OTT but it works and is quiet.  You will have to do it yourself as most exhaust shops will look at you as if you have two heads.

 

Another option would be twin 2.5 with a narrow x pipe at the gearbox extension housing back to twin 2.5" straight throughs at original muffler location dumped at the diff.  This is the set up that I will be running on the roller cam speedway engine.  I run the above set up on my current flat tappet motor. 

 

Both these are well and truly out there designs but they are built on sound theory and not just what makes a street car go fast or what is easy for the exhaust shop. 

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gonzo would be another guy to talk to, he did the pipes in sevos TD garrys TE both those cars did 11s before 2000 most dont know about them as garry has kids and does not play much and stevo sold his and went back to a V8 his engine is still going around in a little red TD XLE runs low 12s and is a street driven car that runs on 98fuel 

 

that being said they did not make there pipes as most say they should be. most talk about long primerys and short seconderys all these pipes are the other way around mine are 1 7/8 off the port into 2 1/4 seconderrys and 3 inch colector and a so long they finnish under the drivers seat and i ran a 3inch system and a hooker centre offset it was noisy that for sure but very good gains over the genies and 2 1/2 that was under there it was like 15 18 rwhp over the 2 1/2inch one with no tuning

 

ask ken if you can copy his pipes? they must work  

 

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All I'm about to type is just my own personal opinion.

Header design is what makes or breaks an engine, what you want is to have a primary and secondary pipe size and length that allows the maximum exhaust gas velocity with no restriction, the size and length is determined by the complete combination as well as it's intended use and rev range, this when done correctly will scavenge the cylinder completely of exhaust gasses and will start pulling in intake charge during the overlap period and is very important to a good cylinder fill, the best way to tell if you have it correct is that the intake runner/port will stay clean, when you see the dirty black shit in there that is reversion and exhaust gas entering the intake during overlap and polluting the intake charge.

The intended use is very important for an inline 6, as Ando mentioned Sly's intended use would require more volume of pipe, the way I would do this is to use the same design as Jason's headers, 6-3-1 setup, this allows you to use the correct size primaries and secondaries but the extra secondary gives the extra volume required for the higher constant revs that this engine will be doing.

 

2820bc931_zpsb51bbb96.jpg

 

I also agree with Dave about the long primary length on tri-y headers, the primary and secondary are pretty much the same length for best results, also if you can build a set of stepped headers that will be next step also. As for tailpipe sizes I personally would go the single setup like Ando mentioned. It comes down to noise when the headers are correct the bigger the tailpipe the noisier/raspier/droney depending on size and config the setup is. That will all depend on mufflers used and the cam and comp of the engine to how it will sound.

I use the latest Pipemax as my guideline and the results of the program when used truthfully have the dyno results to prove that the math works, if you give me your cam details, comp and rod length I can bust out some figures for you Sly if you want :) and your peak HP rpm also which I'm going to have a guess at around 6500rpm.

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What is your best guess (or target) of your peak HP, peak HP rpm, peak torque rpm? When does your exhaust valve open (deg BBDC)?

 

Just guessing some numbers I think you need 1 5/8" primaries, 2 1/4" secondaries and 3.5" exhaust (after around 350HP a 3" exhaust is going to start to cost you).

 

I will try (time permitting) to come up with more info later.

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What is your best guess (or target) of your peak HP, peak HP rpm, peak torque rpm? When does your exhaust valve open (deg BBDC)?

 

Just guessing some numbers I think you need 1 5/8" primaries, 2 1/4" secondaries and 3.5" exhaust (after around 350HP a 3" exhaust is going to start to cost you).

 

I will try (time permitting) to come up with more info later.

 

seems we are on the same page - both students of Vizard it would seem????

 

Diameter of exhaust valve, inside diameter of current extractors and exhaust port I.D. while your going Sly.......

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Mine and Kens were done by the same guy. his may have a smaller primary pipe but i cant remember, they look different because of fitment into the car mine being a TF is a lot tighter then the TD. Also Rob the 3.5" may be the go but every time Ken's is driven in anger the exhaust is siting on the trailer........LOL!!

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Is there a reason the exhaust has to exit the rear? Can it be a side exit before the rear wheels like a V8 supercar, as this will stop any interference with the tailshaft loops and 4 link.

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Is there a reason the exhaust has to exit the rear? Can it be a side exit before the rear wheels like a V8 supercar, as this will stop any interference with the tailshaft loops and 4 link.

 

It will sound 400,000,000,000,000 times better with the mufflers right at the rear valance and I need it somewhat legal so side exit is out.It is too short by about 60-80mm from last rear opening memory.Yes been there done that.

 

To hear this NAT ASP car in the flesh gives any straight man a instant hard on

 

 

There is PLENTY of room for the exhaust to go under the diff and the front 4 link cross member is already notched to accept the twin exhaust and as Ando stated there is no spare wheel well anymore so I have ALOT of room after the diff aswell so finding space for fitment will not be a issue just the current 3" I have doesn't fit the car anymore.

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Now Stu and Smithy at Vintage racing prefer tri y's and concentrate on the collectors and sizing more.I did ask if either was keen to do so and they both said they could and would If I really wanted but they have had better results with the tri y's.Go figure...

 

So I have a ex port size of 1.29

 

extractor port of 1.45 

 

valve of 1.56

 

duration @ 50th of 275

 

lift of 709 (684 minus rocker clearance,see it's not that big)

 

12.4 comp

 

6.25 rod

 

3x50mm webers

 

250 shot of fogger...

 

Knock your selves out...

 

 

 

 

 

 

 

 

 

 

OK maybe no gas but the rest is true...and I'm going to have a shower to get all this bog dust off me and clean up to see if I can pull a root later.

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gonzo would be another guy to talk to,

 

ask ken if you can copy his pipes? they must work

 

 

Last I head he was on the run up in QLD and all but in jail...yes I know who he is and he even did allot of the Shepp boys cars including Sam's GT.The sound is insane...

 

Pretty easy to copy as I already know what he has...Fat Les Pipes and a single 3.5" street system using the 180 degree scavenging system.1-6 2-5 3-4 all 180 degree's apart into a common collector.Done right they look sexy as too. 

 

Yes going for a wash now...

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Well I think your primary sizing is spot on, as to length well I reckon pacemaker know their stuff.  I would highly recommend 2 1/4 secondaries at the length I prescribed.  After that I don't really care as long as it is no smaller than 3.5", mandrel bent and as long as you can before it sees a muffler.  I like the idea of rear exit if it is achievable without too many bends - but then again you don't have a spare wheel recess to worry about anymore.  If you want to knock the noise down run a muffler in the original location and then a moroso spiral flow muffler at the very back.  Gonzo used to make his own resonator very similar to the moroso units.  I highly recommend the Borla muffler if you can afford them.  They make MORE power than open headers - proven time and time again in the US. 

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Now Stu and Smithy at Vintage racing prefer tri y's and concentrate on the collectors and sizing more.I did ask if either was keen I would do so and they both said they could and would If I really wanted but they have had better results with the tri y's.Go figure...

 

So I have a ex port size of 1.29

 

extractor port of 1.45 

 

valve of 1.56

 

duration @ 50th of 275

 

lift of 709 (684 minus rocker clearance,see it's not that big)

 

12.4 comp

 

6.25 rod

 

3x50mm webers

 

250 shot of fogger...

 

Knock your selves out...

 

 

 

 

 

 

 

 

 

 

OK maybe no gas but the rest is true...and I'm going to have a shower to get all this bog dust off me and clean up to see if I can pull a root later.

 

 

LOL. Not sure about washing the bog dust off making a difference bud. I come home covered in that shit most days and it does SFA to bettering my chances by showering! Probably have a better chance if you do the dishes bro!

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Need cam timing if you want length estimates (for what they are worth, diameters are more important).

Didnt bother with the timing specs when I got the cam, I was happy enough to finally get it done after chasing a grinder who was on the same page.

 

709 lift 275 @50th 106 lobe sep on a 104 centreline is more or less what I have.And no I didn't measure it when I set the cam timing.EDIT...yes the cam was dialled in correctly though,took like 5-6hrs to get it right...grrrrrrrrr

 

Funny enough the guy who helped design the cam suggested the twin 2.5 as his preferred option based on his findings with my engine details.He builds 10.5 outlaw cars in the US and will do a Fox body for me 1 day when Im rich.

 

But at this stage Im happy to try to learn and get options and opinions from those who know as it helps make the decission easier and or gives me options to try at worst.

 

I hope this thread helps alot more than just me

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This is the results I got with your specs, assuming 220cfm intake flow with manifold and carb and a 1.84in intake valve.

These are the specs for a 6-3-1 design with a stepped secondary pipe for higher rpm HP in the rev range of 4500 to 7000 with a muffler, the pipe sizes are outside diameter.

primary pipe 1.68in diameter with a length of 15.8in to 17.1in

first step in the secondary 1.805in diameter with a length of 7.9in to 8.5in

second step in the secondary 1.93in diameter with a length of 7.9in to 8.5in

megaphone collector tapered from 2.1in to 3.1in at 17.4in long

 

exhaust port opening cross sectional area of 1.752in

exhaust min cross sectional area of 1.467in

 

Your engines predicted HP with everything tuned perfectly is around the 380fwhp mark and 340ft/lbs of torque

 

Hope this gives you an idea and I really press my opinion of running the same style pipes as Jason with the 6-3-1.

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I have a set of old genie 6 -3 -1 extactors to suit XF here if you need something to copy off.  I am led to believe they are a bit rare and someone once said they were genie 'speedway' extractors.  I'm not sure on that one.  I have never tried them. 

 

The boys run a custom set of  6 into 1 on their speedway car and I know of one other top XF competitor who runs the same set up.  Awesome looking set of pipes, all same length and HPC coated with EGT probes.  very horn. 

 

EGT probes are good for tuning - but then again so is your AFR gauge and with an individual runner manifold EGT's should be pretty even. 

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Re-ran some numbers and you are close to wanting 1 3/4" primarys.

 

Two options both are 6-2-1 configuration, the other configuration doesn't change much (not sure what the support for the 6-3-1 is based on really). For both options the tail pipe can split into a twin system after the collector. As Ando said push the mufflers back as far as possible. Both are for peak HP at 6,500 rpm. If you think it is higher you can shorten the primary and secondary lengths a bit.

 

With your big cam it is boarder line whether you should use baffle or merge type collectors (I would go for merge purely based on what I have read) for between your primaries and secondaries. If you use merge type aim for a 10deg tapper.

 

Don't stress about the lengths too much for the primaries and secondaries but they should be a pretty good target.

 

Option 1 Peak Torque Under 4,500rpm:

 

Primary Pipes: 1 5/8", 25" long

Secondary Pipes: 2 1/4", 12" long

Collector: Type Venturi merge, Min Diameter 2 3/4", Nozzle length (tapper from secondaries) 5" (or ~10deg taper), Diffuser (Min Diameter to Tail Pipe) length 2.7" (or ~8deg taper)

Tail Pipe/Collector Outlet Dia: 3.5" (could get away with 3 1/4" but going bigger with the correct collector costs nothing, if you choose to not use 3.5" it changes your collector diffuser length only)

 

Option 2: Peak Torque at or over 4,500rpm:

 

Primary Pipes: 1 3/4", 25" long

Secondary Pipes: 2 3/8", 12.5" long

Collector: Type Venturi merge, Min Diameter 2 7/8", Nozzle length (tapper from secondaries) 5.3" (or ~10deg taper), Diffuser (Min Diameter to Tail Pipe) length 2.25" (or ~8deg taper)

Tail Pipe/Collector Outlet Dia: 3.5"

 

This is my own approach based mainly on my understanding of acoustic tuning, what I have read and dyno. comparisons of others (I have not tested it myself as it cost $$$). I have PipeMax, but I do not use it. Interestingly Clevo’s primary diameter (most important in my opinion) and total extractor length are about the same as mine (it is the combined length that you tune for). PipeMax seems to use a 50-50 split whereas I split my primary and secondary lengths to target two octaves, I doubt you would notice the difference but I think the 50-50 split is odd.

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Another silly idea that I have always wondered with hypo sixes is why not run try y design extractors but instead on the final merge continue the secondaries into a twin exhaust with a taper from secondary size into exhaust size.

 

Also with the intended operating rpm range and setup of this engine surely 13/4 primaries are needed.

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The collector allows you to run larger diameter exhausts and is used for tunning purposes (which requires at least two pipes). Without the collector it is like having massively long secondaries, including the taper just makes them stepped secondaries.

 

What are your 1 3/4" primaries based on??

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Mat the reason I personally press for the extra secondary pipe is for secondary volume on a constant high revving engine, with 3 primaries going into 1 secondary you naturally up the size of the secondary for extra flow volume but then you have changed from a small primary to a much larger secondary which in my opinion is too big of a step up in size for scavaging because of the dramatic change in gas speed between the 2 sizes. with the extra secondary you are keeping a better ratio change between the primary and secondary with a smaller secondary but because there are 3 you actually have more volume in total but keep the gas speed up in each secondary.

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